The subject matter disclosed herein relates to estimation of coronary flow and fractional flow reserve using imaging techniques.
Non-invasive imaging technologies allow images of the internal structures or features of a patient to be obtained without performing an invasive procedure on the patient. In particular, such non-invasive imaging technologies rely on various physical principles, such as the differential transmission of X-rays through the target volume or the reflection of acoustic waves, to acquire data and to construct images or otherwise represent the observed internal features of the patient.
For example, computed tomography (CT), including coronary computed tomography angiography (CCTA) devices and techniques, is an imaging technology based on the observed transmission of X-rays through the patient for a range of angular positions that is sufficient for image reconstruction. With the introduction of multi-slice CT scanners and faster rotation speeds, it has become possible to generate useful images of the heart. By way of example, computed tomography can accurately determine the reduction in lumen diameter due to a coronary artery stenosis (i.e., a narrowing of the coronary vessel, such as due to atherosclerotic plaque). However, anatomic presence or identification of a stenosis does not necessarily translate to actual functional significance, i.e. oxygen deprivation to myocardial tissue, to the patient.
With this in mind, the concept of fractional flow reserve was introduced to address this issue. Fractional flow reserve is the ratio of pressure distal to the stenosis to the pressure proximal to it and measures the hemodynamic resistance of the stenosis relative to the resistance of the coronary microcirculation. In conventional approaches, fractional flow reserve is measured at the time of invasive angiography by inserting a tiny guide wire through a standard diagnostic catheter. A sensor at the tip of the wire measures pressure. Pressure is measured both distal and proximal to the stenosis in the coronary artery to estimate fractional flow reserve. Such approaches, however, may be undesirable due to their invasive nature.